A Day on the Green at Kings Park, headlined by John Farnham and featuring Mondo Rock, Kate Ceberano and The Badloves, has already been rescheduled to February 4.

The 2017 IGA Carols by Candlelight for Variety, which was due to take place at Langley Park last night, has been cancelled along with other, smaller outdoor events across Perth.

Wind picked up the tarp as they struggled to fix it into place. (9NEWS) ()Workers struggled to cover the pitch as rain bucketed down at the WACA yesterday. (9NEWS) ()

BoM says a deep, slow-moving low pressure system is expected to pass close to the southwest corner of WA through to this afternoon, along with an associated cold front.

Rain and winds with gusts of up to 100km/h are expected from Margaret River to Walpole on Sunday afternoon before extending over the South West Land Division in the evening. Low-lying coastal regions would be at risk of flooding as a result of higher than normal tides.

The affected areas include Albany, Bunbury, Busselton, Mandurah, Manjimup, Margaret River and Perth.

Elsewhere in Australia, SA and NSW are set for a scorching week, with some areas bracing for 45C days.

New South Wales is expecting sky high temperatures this week, with a wide range of predictions across Sydney, but those in central NSW and western Sydney are set to feel the worst of the heat.

A maximum of 45C is predicted to hit Ivanhoe in central NSW today and tomorrow. The splintering heat could even break the town’s record for the hottest December day in 29 years of records. The mercury rose to 45.8C on December 31 in 2005, Weatherzone meteorologist Kim Westcott told 9news.com.au.

BoM's weather forecast for today across the nation. ()

In Broken Hill on the state border the temperature is expected to rise to 44.2 tomorrow – a whopping 13C above the town’s 31.5C December average.

The town’s hottest December day in roughly 29 years of records was 44.2 in 2005.

“It will potentially be the hottest December day for Broken Hill, it got close last week on the 13th when it got to 42.1, but this might be the one,” Ms Westcott said.

However, things are even “looking to be really hot” back east in Sydney, Ms Westcott added.

“The forecast for Penrith is 43C tomorrow and it’s 42C on Wednesday,” she said.

“The Penrith December average is 29.4C.”

Penrith had its hottest day in about eight years on December 13 when the mercury rose to 43.5C.

Ms Westcott said there will be “a big split of temperatures over Tuesday and Wednesday between east and west” in Sydney where it could be up to 10C cooler, but it will still be very warm.

Weatherzone's Christmas forecast. ()

The maximum expected in the city today is 33C, with 33C predicted tomorrow and 34C on Wednesday, before a cool relief sets in.

“For Sydney Thursday’s going to be showery and cool and 25C and that’s the same in the western suburbs as well, so there will be a big drop,” Ms Westcott said.

She said it will warm up “as we lead up to Christmas, on Saturday and Sunday the 23rd and the 24th” before cooling down again on Christmas day – which is predicted to be cloudy and 24C in Sydney.

It’s expected to be sweltering in South Australia as well.

“Today is going to be the state’s hot day, even Adelaide itself is going to be 38C to 40C,” Ms Westcott said.

“It’s still going to be quite hot at midnight despite all that cloud that’s coming in with the slow pressure trough.

“But this is their final hot day and after that you’ve got a few milder days.”

However, the relief will be short lived with “two quite hot days again on the 22nd and the 23rd”.

Last Christmas Adelaide suffered through a 41.3C day, but Ms Westcott said they’re in for a much easier day this time around.

“For Christmas, unlike last year which was extremely hot, it will be a beautiful reprieve, with Adelaide looking at about 26C and a mostly sunny day,” she said.